Symfony2 how to validate unique email using validator component

Im creating an application that creates users from a CSV file, so there is no Forms. i'm using the symfony validator component to validate the data inside the controller. so far ive created a helper function that takes in the data and the constraints and returns out the error if any. here is what i mean.

Here i need to check if the email specified in the CSV already exists in the database, for this im assuming that UniqueEntity has to be used. It has an associated class called UniqueEntityValidator. The amazing thing is that the Validator Component has a feature that automatically checks the locale and displays the error messages in that language!! (i'm guessing its through the ConstraintViolation object). I would like to utilize this feature instead of the bland

findOneBy()

to query the database and check if the email already exists and returning with an error message using (comparatively) messy xliff files.

so! the question is how to validate for unique email in the database using the validator component's validator service

edit: in the above code

$associativerow['email']

is a string, but in practice i can have it as a

User

object if necessary, you can have the liberty to assume its an entity object if needed!